According to TMZ’s sources, Swift and Harris’ relationship fell apart because “he disrespected her when the song was released.”

Knowing the song would be a hit and not wanting their collaboration to overshadow it, Swift, who kept the publishing rights, used the pseudonym Nils Sjoberg on the credits.

Calvin released the song on April 29 with Rihanna and, as they imagined, it became an instant hit. It’s been at #1 or #2 on the Dance/Electronic chart for 9 weeks, and is #5 on the Billboard 100, according to TMZ.

So, what’s the problem you ask? Well, when the song was released, Harris appeared on Ryan Seacrest’s radio show and told Seacrest he doesn’t plan to ever work with Swift again.

You know we haven’t even spoken about it. I can’t see it happening though.

According to TMZ, that hurt Swift’s feelings; she felt he took it too far. A source called this April occurrence the “breaking point in the relationship,” said TMZ.

So, when news broke of Swift’s secret collaboration, at first, Harris was all smiles (or, upside down smiles).